Rotary power lawn mowers are widely used by homeowners and the like for cutting grass to maintain the appearance of the lawns about residences, etc. Such mowers typically employ an elongated blade of unitary construction having cutting edges at opposing distal ends thereof which is adapted for rotating horizontally at high speed within a housing intended to prevent injury to the user and to control the direction of discharge of grass clippings and other debris that may be encountered during operation of the mower. The mower blade is, in general, centrally mounted on a shaft vertically extending through the housing from a gasoline or electric powered motor secured to top of the housing.
It is well known that the effectiveness of the mower for cutting grass generally depends on the sharpness of the cutting edges located at each end of the rotating blade as well as on the balance of the rotating blade. Due to the high speed of rotation at which cutting blades of rotary type lawn mowers are operated and the close proximity of the blade to stones, tree roots and the like on the ground, frequent maintenance of the blade sharpness and balance is required for grass cutting effectiveness. Heretofore, such maintenance typically required removal of the blade from the motor shaft for sharpening, straightening, balancing, etc , and then, of course, remounting on the mower.
Numerous suggestions have been made over the years relating to means for sharpening the rotary mower blades and/or replacing the cutting edges thereof without removing the blade from its mounting on the motor shaft, such as disclosed, for example, in U.S. Pat. Nos. 3,101,629; 3,243,944; 3,447,291; 3,563,015; 3,683,606; 3,782,039; 3,762,138; 3,949,541; 4,043,104; 4,229,933; 4,285,169; 4,375,148; 4,471,603; 4,509,316; 4,594,843; 4.651,510; 4,715,173; and 4,750,320. However, the prior art disclosures generally involve blade sharpening devices that incorporate additional structures on the mower which are costly and complex and/or various types of blade assemblies with detachable cutting edges that generally employ specially configured mounting blades and/or cutting members which require special tools, separate fastening means and/or a significant amount of manipulation by the user to assure the safety of their use. Accordingly, the desirability of a blade assembly configuration that would provide means for quickly replacing and securely mounting the cutting edges of a rotary lawn mower blade without the need for special tools and, preferably, would provide more than one set of replacement cutting edges would be evident.